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Abstract:

A device for error monitoring in an internal combustion engine system is
provided. The internal combustion engine is supplied with air at a
volumetric efficiency indicating the ratio of a real volume flow of air
in the internal combustion engine to an ideal, theoretically possible,
volume flow of air in the internal combustion engine. The device for
error monitoring is configured to determine an error in the engine system
when a difference between a measured volumetric efficiency and an
estimated volumetric efficiency exceeds a predetermined absolute value.

Claims:

1. A device for error monitoring in an engine system having an internal
combustion engine, the engine system being configured to supply the
internal combustion engine with air at a volumetric efficiency indicating
the ratio of actual volume flow of air in the internal combustion engine
to an ideal, theoretically possible, volume flow of air in the internal
combustion engine, the device comprising: a detection system for at least
one of measuring and estimating the volumetric efficiency; and an
error-monitoring unit configured to determine an error in the engine
system based on the at least one of the measured volumetric efficiency
and the estimated volumetric efficiency.

2. The device as recited in claim 1, wherein: the detection system
includes a measuring device configured to measure the volumetric
efficiency and an estimation device configured to estimate the volumetric
efficiency; and the error-monitoring unit includes a checking device
configured to check the measured volumetric efficiency for plausibility
based on the estimated volumetric efficiency.

3. The device as recited in claim 2, wherein the device is a vehicle
diagnostic system for a vehicle driven by the internal combustion engine.

4. The device as recited in claim 2, wherein the checking device is
configured to: (i) calculate a difference between the measured volumetric
efficiency and the estimated volumetric efficiency; and (ii) output an
error signal when the difference exceeds a predetermined absolute value.

5. An engine system for driving a vehicle, comprising: an internal
combustion engine configured to receive a charge of fresh air for a fuel
combustion and to output exhaust gas after the fuel combustion, wherein
the internal combustion engine is supplied with the fresh air at a
volumetric efficiency indicating the ratio of actual volume flow of air
in the internal combustion engine to an ideal, theoretically possible,
volume flow of air in the internal combustion engine; and an
error-monitoring system including: (i) a measuring device configured to
measure the volumetric efficiency and an estimation device configured to
estimate the volumetric efficiency; and (ii) a checking device configured
to output an error signal when a difference between the measured
volumetric efficiency and the estimated volumetric efficiency exceeds a
predetermined absolute value.

6. The engine system as recited in claim 5, further comprising: at least
one intake system configured to take in fresh air into the engine system;
at least one exhaust gas recirculation system configured to recirculate
at least a portion of the exhaust gas into the internal combustion
engine; and at least one mixing unit configured to mix the fresh air and
the recirculated exhaust gas.

7. The engine system as recited in claim 6, wherein a device for modeling
the volumetric efficiency based on the pressure of the mixture of the
fresh air and the recirculated exhaust gas, the temperature of the
mixture of the fresh air and the recirculated exhaust gas, and the
rotational speed of the internal combustion engine is provided.

8. The engine system as recited in claim 6, wherein the volumetric
efficiency is estimated based on an enthalpy flow balance between the
enthalpy flow of the fresh air and the enthalpy flow of the recirculated
exhaust gas.

9. The engine system as recited in claim 8, wherein the enthalpy flow of
the recirculated exhaust gas is estimated based on a mass flow of the
recirculated exhaust gas through the exhaust gas recirculation system.

10. The engine system as recited in claim 8, wherein the enthalpy flow of
the recirculated exhaust gas is estimated based on a mass flow of the
recirculated exhaust gas through the mixing unit.

11. A method for error monitoring in an engine system having an internal
combustion engine, the engine system being configured to supply the
internal combustion engine with air at a volumetric efficiency indicating
the ratio of actual volume flow of air in the internal combustion engine
to an ideal, theoretically possible, volume flow of air in the internal
combustion engine, the method comprising: measuring the volumetric
efficiency; estimating the volumetric efficiency; and checking the
measured volumetric efficiency for plausibility based on the estimated
volumetric efficiency, wherein an error is detected when a difference
between the measured volumetric efficiency and the estimated volumetric
efficiency exceeds a predetermined absolute value.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an on board diagnostic system in a
vehicle having an internal combustion engine.

[0003] 2. Description of the Related Art

[0004] On board diagnostic systems are vehicle diagnostic systems which
monitor all emission-influencing systems during the operation and store
possibly arising errors in a memory so that they may be queried by a
specialized repair shop and, if necessary, eliminated.

[0005] Most of the previously known functions in this type of on board
diagnostic system measure a characteristic within the internal combustion
engine at operating points, which occur rarely in most cases, and compare
this characteristic to the nominal case. Alternatively, a so-called
intrusive test may be carried out. This test is an intervention into the
system at certain operating points to provide the conditions for the
measurement. In any case, the situation in the nominal case must be saved
so that the measurement may be compared to it. However, a memory is not
only expensive, it also needs space which is available only to a limited
extent in the engine control of a vehicle.

BRIEF SUMMARY OF THE INVENTION

[0006] According to one first aspect of the present invention, a device
for error monitoring in an engine system having an internal combustion
engine is provided, the engine system being designed to supply the
internal combustion engine with air at a volumetric efficiency, the
volumetric efficiency indicating the ratio of a real volume flow of air
in the internal combustion engine to an ideal, theoretically possible,
volume flow of air in the internal combustion engine, the device being
designed to determine an error in the engine system based on the
volumetric efficiency.

[0007] The device according to the present invention has the advantage
that it requires less memory space as compared to conventional devices
for error monitoring in an engine system. This is achieved by selecting
for the characteristic of error recognition the volumetric efficiency as
a variable in the engine system, the variable being necessary, e.g., for
operating the filling control, regardless of the device for error
monitoring. In this way, the data do not have to be specifically
determined and stored in the memory for the comparison to the nominal
case. The time constant of the volumetric efficiency
estimation/recognition is approximately in the range of the time constant
of the filling control. In this way, the volumetric efficiency is
available relatively quickly compared to previously known systems. This
expands the ranges in which monitoring is possible since it is also
conceivable to use the volumetric efficiency recognition during
relatively short controlled operating modes. The volumetric efficiency is
calculated by being compared to a variable which was previously applied
for the nominal state (normal vehicle operation). It is thus not
necessary to separately apply and save the situation in the nominal case.
This reduces the complexity of the application and the storage space
required in the control unit.

[0008] In one embodiment of the present invention, the device may include
the following characteristics:

[0009] a measuring device which is
suitable to measure the volumetric efficiency;

[0010] an estimation
device which is suitable to estimate the volumetric efficiency; and

[0011] a checking device which is suitable to check the measured
volumetric efficiency for plausibility based on the estimated volumetric
efficiency.

[0012] The estimation device may estimate the volumetric efficiency in
particular based on a provided model of the internal combustion engine.

[0013] In one preferred embodiment of the present invention, the device is
a vehicle diagnostic system for a vehicle driven by the internal
combustion engine. Vehicle diagnostic systems, such as on board
diagnostic systems, are devices in a vehicle which are required by law
and from which the function of the vehicle itself does not benefit at
all. They are only used to comply with the regulations for environmental
protection. The device according to the present invention may be used to
carry out this type of vehicle diagnostic system based on the
characteristics which must be calculated anyway for the vehicle to
function properly, thus saving resources in the engine control unit.

[0014] In another preferred embodiment of the present invention, the
checking device for the plausibility check may be provided to calculate a
difference between the measured volumetric efficiency and the estimated
volumetric efficiency, and to output an error when the difference exceeds
a predetermined absolute value. The comparison between the difference and
a predetermined absolute value makes it possible to introduce tolerances
into the system which allow those deviations from the nominal state to be
ignored which do not result in a noteworthy malfunction of the vehicle.

[0015] According to another aspect of the present invention, an engine
system includes, for driving a vehicle, an internal combustion engine for
receiving an intake charge of fresh air for a fuel combustion and for
outputting exhaust gas after the fuel combustion, and a device according
to the present invention for outputting an error when the plausibility
check of the volumetric efficiency factor results in a deviation between
the measured and the estimated volumetric efficiency factor. In the
engine system according to the present invention, erroneous exhaust gas
values may easily be recognized, without having to implement additional
measuring systems in the engine system.

[0016] In one refinement of the present invention, the engine system
includes an intake system for taking in gas into the engine system, an
exhaust gas recirculation for recirculating at least a portion of the
exhaust gas into the internal combustion engine, and a mixing section for
mixing the fresh air and the recirculated exhaust gas for filling. In
this way, an exhaust gas recirculation is provided which makes it
possible to reduce the portions of discharged harmful agents in the
exhaust gas, such as nitrogen oxides.

[0017] In another refinement, the device for measuring the volumetric
efficiency based on the pressure, the temperature, and the rotational
speed may be provided in the internal combustion engine. This makes it
possible to measure the volumetric efficiency with the aid of sensors
which are already present in the internal combustion engine.

[0018] In an alternative or additional embodiment, the device for
estimating the volumetric efficiency based on an enthalpy flow balance
between the enthalpy flow of the gas taken in and the enthalpy flow of
the recirculated exhaust gas may be provided. The enthalpy flow balance
may be ascertained in the engine system with the aid of already present
sensors so that the boundary conditions for the estimation of the
volumetric efficiency are determinable without further technical changes
in the engine system.

[0019] In another embodiment of the present invention, the device for
estimating the enthalpy flow of the recirculated exhaust gas based on a
mass flow of the recirculated exhaust gas through the exhaust gas
recirculation may be provided. This estimation is, for example, possible
in a simple manner based on the measured variables such as the position
signal/actuating signal present at the valve in the exhaust gas
recirculation.

[0020] In an additional embodiment of the present invention, the device
for estimating the enthalpy flow of the recirculated exhaust gas based on
a mass flow of the recirculated exhaust gas through the mixing section
may be provided. This estimation is possible in a simple manner via an
enthalpy flow balance between the enthalpy flow of the gas taken in and
the enthalpy flow in the internal combustion engine.

[0021] In one preferred embodiment of the present invention, the device
for selecting the enthalpy flow calculated based on the actuating signal
of the exhaust gas recirculation valve or the enthalpy flow modeled based
on the enthalpy flow balance at the mixing location may be provided for
the estimation of the volumetric efficiency. The signal quality of the
volumetric efficiency with regard to the signal noise ratio is always
equally good since the volumetric efficiency is calculated by using
different sources of information. Here, insensitive ranges or operating
modes are suppressed so that a signal of adequate quality is always
available. When calculating the characteristics in previously known on
board diagnostic systems, these insensitive ranges in which the signal
is, for example, strongly affected by noise must be explicitly blended
out with the aid of operating range restrictions.

[0022] According to another aspect of the present invention, a method for
error monitoring in an engine system, which fills a filling of gas into
an internal combustion engine at a volumetric efficiency, the volumetric
efficiency indicating the ratio of the real volume flow in the engine to
the ideal (theoretically possible) volume flow in the engine, includes
the following steps: measuring the volumetric efficiency, estimating the
volumetric efficiency, and checking the measured volumetric efficiency
for plausibility based on the estimated volumetric efficiency.

[0025] FIG. 3 shows a block diagram for checking a measured volumetric
efficiency based on an estimated volumetric efficiency.

DETAILED DESCRIPTION OF THE INVENTION

[0026] Reference is made to FIG. 1. An engine system 2 having an internal
combustion engine 4 is illustrated in FIG. 1.

[0027] Fresh air 10 is supplied via an air supply 6 to internal combustion
engine 4 initially in the flow direction identified by arrows. An air
mass flow measuring device 12, in the form of a hot film air mass flow
sensor, for example, which measures fresh air mass flow 11 and outputs it
to an engine control 13, is situated in air supply 6. Alternatively, the
fresh air supply may also be modeled and the necessary sensor may be
modeled at another place in the air system.

[0029] Downstream from air mass flow measuring device 12 in the flow
direction, one or multiple compressors 14 may be situated in air supply
6. The compressed air is provided with reference numeral 15.

[0030] The section of air supply 6 downstream from compressor 14 in the
flow direction is referred to in the following as intake manifold 16.
Exhaust gas 20 may be supplied to intake manifold 16 in a junction 17 via
an exhaust gas recirculation channel 18 from an exhaust gas system 22 of
engine system 2. Engine intake air 19 resulting therefrom is supplied to
internal combustion engine 4. The flow directions of exhaust gas 20 in
exhaust gas system 22 and engine intake air 19 are identified by an
arrow. The recirculated exhaust gas is provided with reference numeral 21
whose flow direction is also identified by an arrow. Fuel may be injected
into engine intake air 19 or into compressed air 15 as is the case in
some gasoline engines, for example. Alternatively, the fuel may also be
injected directly into the internal combustion engine as is customary for
a diesel engine.

[0031] In the flow direction downstream from junction 17 of exhaust gas
recirculation channel 18 into intake manifold 16, a pressure sensor 24
and a temperature sensor 26 are situated in intake manifold 16.
Temperature sensor 26 and pressure sensor 24 ascertain temperature 28 and
pressure 30 of supplied and compressed air 15, which, if necessary, is
enriched with recirculated exhaust gas 21, and output them to engine
control 13. The pressure and temperature information may also be modeled
on the basis of other, placed sensors.

[0032] An exhaust gas recirculation valve 32 is situated in exhaust gas
recirculation channel 18 to control the quantity of recirculated exhaust
gas 21. As previously described, internal combustion engine 4 has on its
output side exhaust gas system 22 off of which exhaust gas recirculation
channel 18 branches. In the flow direction downstream from the branch-off
of exhaust gas recirculation channel 18 situated in exhaust gas system
22, one or multiple turbines 34 may be situated which drive compressor
14, for example. Furthermore, a rotational speed sensor 36, which
ascertains rotational speed 38 of internal combustion engine 4 and
outputs it to engine control 13, is situated on internal combustion
engine 4.

[0033] The mass flow of engine intake air 19, which is referred to in the
following as the filling is assigned symbol {dot over (m)}F for
subsequent calculations. The filling is yielded from the sum of intake
gas mass flow 11 having symbol {dot over (m)}L, which is, for
example, measured using air mass flow measuring device 12, and the mass
flow of recirculated exhaust gas 18. In addition to the measurement by
air mass flow measuring device 12 in the closed exhaust gas
recirculation, filling {dot over (m)}F may also be calculated as
follows:

m . F = λ a V H n p 2 R T ( 1 )
##EQU00001##

[0034] In equation (1), λa is volumetric efficiency 58 shown in
FIG. 3 and it indicates the ratio of the real volume flow in the engine
to the ideal (theoretically possible) volume flow in the engine. VH
is the swept volume of internal combustion engine 4. n is rotational
speed 38 of internal combustion engine 4. p is pressure 30 in intake
manifold 16 measured by pressure sensor 24. R is the general gas
constant. T is temperature 28, which is measured by temperature sensor 26
or modeled, in intake manifold 16 in the flow direction downstream from
junction 17 of recirculated exhaust gas 18.

[0035] To measure volumetric efficiency 58, exhaust gas recirculation 18
may, for example, be interrupted during a calibration measurement and the
filling may be determined. The measured value for volumetric efficiency
58 is determinable by solving equation (1) according to volumetric
efficiency 58.

[0036] Measured volumetric efficiency 58 is checked for plausibility
according to the present invention. For this purpose, it may, for
example, be estimated one more time and checked based on that. This type
of estimation and check is explained based on FIGS. 2 and 3, as an
example, where elements identical to FIG. 1 are provided with identical
reference numerals and are not described again.

[0037] In FIG. 2, one or multiple compressor(s) 14 separate(s) the air
supply in the engine into a low-pressure area and a high-pressure area.
In the low-pressure area, fresh air 10 taken in is guided via a
low-pressure valve 40 (not shown in FIG. 1) and mixed with a portion of
exhaust gas 22 downstream from turbine 34. The quantity of exhaust gas 22
to be added in the low-pressure area is controlled via a low-pressure
exhaust gas recirculation valve 42. In the high-pressure area, the supply
of compressed fresh air 15 to junction 17 is controlled via a throttle
valve 48 (not shown in FIG. 1).

[0038] FIG. 3 shows the structure diagram of the determination of the
plausibility check of measured volumetric efficiency 58 based on
estimated volumetric efficiency 51. To determine estimated volumetric
efficiency 51, the sequence shown in FIG. 3 includes a balancing section
54 and an estimation section 56. After the estimation, measured
volumetric efficiency 58 is checked in a checking section 57 based on the
estimation.

[0039] In the present embodiment, the estimation of volumetric efficiency
58 is based on the mass flow of recirculated exhaust gas 21, since this
variable is redundantly determinable in most vehicles so that the value
for the mass flow of recirculated exhaust gas 21, which has the greatest
information content, may always be used for the estimation. If, for
example, valve 32 in exhaust gas recirculation channel 18 is closed, but
one of the values for the mass flow of recirculated exhaust gas 21 is
greater than zero, its information content is equal to zero, since the
value is obviously incorrect.

[0040] In balancing section 54, a value 76 is determined for the mass flow
of recirculated exhaust gas 21 as the estimation basis for estimation
section 56. This essentially takes place based on a balancing of the
filling and fresh air mass flow 11. For implementability reasons, not the
mass flows themselves, but the enthalpy flows associated with them, are
balanced, however. To carry out the calculations, pressure 30, measured
volumetric efficiency 58, rotational speed 38, and fresh air mass flow 11
are supplied to balancing section 56 from engine system 2. From a
temperature sensor 26 (shown in FIG. 1), temperature 60 of compressed
fresh air 15 prevails in balancing section 54 upstream from throttle
valve 48, which is assigned symbol TvD. Temperature 61, which is
assigned symbol TA, is detected in the same manner in exhaust gas
recirculation channel 18 and made available to balancing section 54. As
an alternative to the measurement, the temperatures may also be modeled
upstream from throttle valve 48 and in exhaust gas recirculation channel
18.

[0041] The determination of enthalpy flow 62 through throttle valve 48
takes place in balancing section 54 based on a first function 64 having
functional derivative f1, which is assigned symbol {dot over
(h)}L. In f1, fresh air mass flow 11 and temperature 60 of
compressed fresh air 15 upstream from throttle valve 48 are incorporated
according to the following equation:

{dot over (h)}L=f1({dot over (m)}L,TvD) (2)

[0042] Functional derivative f1 of first function 64 may be derived
from a thermodynamic approach to enthalpy flow determination.

[0043] To determine enthalpy flow 65 through internal combustion engine 4,
volume flow 38 through internal combustion engine 4 must initially be
determined, which is assigned symbol {dot over (V)}F. This takes
place in a second function 66 having functional derivative f2 based
on measured volumetric efficiency 58 and rotational speed 38 according to
the following equation:

{dot over (v)}F=f2(λa,n) (3)

[0044] Functional derivative f2 of second function 66 may be derived
from a volume balance in the engine and may be stored in a memory of
engine control 13, for example. Enthalpy flow 65 through internal
combustion engine 4, which is assigned symbol {dot over (h)}F, is
then yielded in balancing section 54 using a third function 70 having
functional derivative f3 based on previously calculated volume flow
68 and pressure 30 in internal combustion engine 4 according to the
following equation:

{dot over (h)}F=f3(p,{dot over (v)}F) (4)

[0045] Functional derivative f3 of third function 70 may be derived
from a thermodynamic approach to enthalpy flow determination.

[0046] To balance enthalpy flow 72 through valve 32 in exhaust gas
recirculation channel 18 having symbol {dot over (h)}A,Balance, it
is assumed in one variant that neither mass nor enthalpy may be stored in
junction 17. Balanced enthalpy flow 72 is then yielded according to the
following equation:

{dot over (h)}A,Bilanz={dot over (h)}L-{dot over (h)}F
(5)

[Bilanz=Balance]

[0047] This equation may be further expanded by memory effects of the
mixing location as well as wall heating processes.

[0048] Subsequently, balanced enthalpy flow 72 is converted using a fourth
function 74 having functional derivative f1 based on temperature 61
in exhaust gas recirculation channel 18 into first value 76 for the mass
flow of recirculated exhaust gas 21, which is assigned symbol {dot over
(m)}A,Balance, according to the following equation:

{dot over (h)}A,Bilanz=f1({dot over (m)}A,Bilanz,TA)
(6)

[Bilanz=Balance]

[0049] In estimation section 56, an estimation of the actual mass flow of
recirculated exhaust gas 21 is carried out based on this first value 76
for the mass flow of recirculated exhaust gas 21 and a second value 78
for mass flow {dot over (m)}A of recirculated exhaust gas 21, which
is assigned symbol {dot over (m)}A,Valve. Second value 78 may, for
example, be determined directly from a measurement of pressure ratio at
exhaust gas recirculation valve 32 using a thermodynamic approach, for
example, with the aid of a throttle equation.

[0050] Ideally, first value 76 and second value 78 for the mass flow of
recirculated exhaust gas 21 are identical. In practice, however, the two
values always deviate slightly from one another. In the previously
mentioned manner, that value 76, 78 is selected for determination of
estimated volumetric efficiency 51 in estimation section 56 whose
information content is greater due to certain boundary conditions. This
selection takes place via an estimation function 80 in estimation section
56, a Kalman filter, for example.

[0051] From estimated mass flow 82 of recirculated exhaust gas 21, output
by estimation function 80, an estimated enthalpy flow 86 through exhaust
gas recirculation channel 18 may be calculated together with temperature
61 in exhaust gas recirculation channel 18 in a fifth function 84, which
is based on functional derivative f1 of equation (2). By balancing
this estimated enthalpy flow 86 of recirculated exhaust gas 21 and
enthalpy flow 62 through throttle valve 48 output from first function 64,
an estimated enthalpy flow 88 through internal combustion engine 4 is
determined in estimation section 56, based on which estimated volumetric
efficiency 51 is finally calculated via pressure 30 in a sixth function
87, which is based on functional derivatives f2, f3.

[0052] In monitoring section 57, measured volumetric efficiency 58 is
checked for plausibility by a comparison based on estimated volumetric
efficiency 51. The comparison takes place by the formation of a
difference 89 which is checked for its level in a filter 90. If measured
volumetric efficiency 58 deviates too excessively from estimated
volumetric efficiency 51, an error 92 is finally output by monitoring
section 57.

[0053] According to the present invention, the volumetric efficiency is
used for error diagnosis in a vehicle, since it is calculated anyway
within the scope of the control systems present in the vehicle, thus
allowing not only for a diagnosis at smaller measurement complexity but
also providing the diagnosis results on a time constant of the control
which uses the volumetric efficiency.